U.S. patent number 6,385,323 [Application Number 09/310,125] was granted by the patent office on 2002-05-07 for hearing aid with automatic microphone balancing and method for operating a hearing aid with automatic microphone balancing.
This patent grant is currently assigned to Siemens Audiologische Technik GmbH. Invention is credited to Fred Zoels.
United States Patent |
6,385,323 |
Zoels |
May 7, 2002 |
Hearing aid with automatic microphone balancing and method for
operating a hearing aid with automatic microphone balancing
Abstract
A hearing aid has a signal processing unit, an earphone and at
least two microphones whose output signals are subtracted from one
another in a first difference element in order to achieve a
directional microphone characteristic, and a difference element
subtracts average values of the output signals of the microphones
and supplies a signal to an analysis/control unit for controlling
the amplification of the output signal of at least one of the
microphones that follows the second difference element. In a method
for the operation of a hearing aid having automatic microphone
balancing, following formation of average values proceeding from
the output signals of the microphones, the deviation of the average
values from one another is identified and the amplification of at
least one output signal of a microphone is adjusted until
coincidence of the average values occurs.
Inventors: |
Zoels; Fred (Altenthann,
DE) |
Assignee: |
Siemens Audiologische Technik
GmbH (Erlangen, DE)
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Family
ID: |
7868000 |
Appl.
No.: |
09/310,125 |
Filed: |
May 12, 1999 |
Foreign Application Priority Data
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May 15, 1998 [DE] |
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198 22 021 |
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Current U.S.
Class: |
381/313; 381/120;
381/57; 381/91; 381/92 |
Current CPC
Class: |
H04R
25/407 (20130101); H04R 29/006 (20130101) |
Current International
Class: |
H04R
25/00 (20060101); H04R 025/00 () |
Field of
Search: |
;381/312,313,314,57-58,91-92,95,102,104,107,120-122,170,356-358,320-321,83,93 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Audio Zoom-Signal Processing for Improved Communications in
Noise," Bachler et al., Phonak Focus, vol. 18 (1995)..
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Primary Examiner: Tran; Sinh
Assistant Examiner: Dabney; P.
Attorney, Agent or Firm: Schiff Hardin & Waite
Claims
I claim as my invention:
1. A hearing aid comprising:
at least a first microphone and a second microphone which
respectively produce microphone output signals;
a first difference-forming element, supplied with said output
signals from said first and second microphones, for subtracting
said output signals from each other to form an output signal
representing a directional microphone characteristic;
an earphone supplied with said output signal from said first
difference-forming element;
a second difference-forming element wherein average values of said
output signals of said first and second microphones are subtracted
from each other to produce an output; and
an analysis and control unit supplied with said output from said
second difference-forming element which controls amplification of
the output signal of at least one of said first microphone and said
second microphone.
2. A hearing aid as claimed in claim 1 further comprising at least
one adjustable amplifier, supplied with an output signal from said
analysis and control unit, connected between one of said first
microphone and said second microphone and said first
difference-forming unit.
3. A hearing aid as claimed in claim 1 further comprising a first
rectifier connected between said first microphone and said second
difference-forming unit for rectifying said output signal of said
first microphone, and a second rectifier connected between said
second microphone and said second difference-forming unit for
rectifying said second output signal from said second
microphone.
4. A hearing aid as claimed in claim 1 wherein said analysis and
control unit comprises an I-regulator.
5. A hearing aid as claimed in claim 1 wherein said analysis and
control unit comprises a PI regulator.
6. A hearing aid as claimed in claim 1 further comprising a level
acquisition element connected between said first and second
microphones and said second difference-forming element for
identifying a level of the output signals of said first and second
microphones and for passing said output signals of said first and
second microphones to said second difference-forming element
dependent on said level.
7. A hearing aid as claimed in claim 6 wherein said level
acquisition element comprises a threshold element.
8. A hearing aid as claimed in claim 1 wherein said output signal
of said first and second microphones each have a frequency range,
and further comprising a filter element connected between said
first and second microphones and said second difference-forming
element for limiting a frequency of said output signals of said
first and second microphones supplied to said second
difference-forming element.
9. In a hearing aid having at least first and second microphones,
each of which emits an output signal, a first difference-forming
element supplied with the output signals of said first and second
microphones for subtracting said output signals from each other to
produce an output signal representing a directional microphone
characteristic, and an earphone supplied with the output signal
from said first difference-forming element, a method for
automatically balancing the output signals from said first and
second microphones comprising the steps of:
forming a first average value of the output signal from said first
microphone and forming a second average value of the output signal
from said second microphone;
identifying any deviation of said first average value from said
second average value; and
amplifying at least one of the respective output signals from said
first and second microphones until said average values
coincide.
10. A method as claimed in claim 9 wherein the step of forming said
first average value comprises forming an average value of RMS
values of said output of said first microphone and wherein the step
of forming said second average value comprises forming an average
value of RMS values of said output signal from said second
microphone.
11. A method as claimed in claim 9 wherein the step of forming said
first average value comprises forming an average value of peak
values of said output of said first microphone and wherein the step
of forming said second average value comprises forming an average
value of peak values of said output signal from said second
microphone.
12. A method as claimed in claim 9 comprising the additional step
of identifying one of said first and second microphones as being a
less sensitive microphone, and wherein the step of amplifying the
output signal of at least one of said first and second microphones
comprises amplifying the output signal from said less sensitive
microphone.
13. A method as claimed in claim 12 wherein said hearing aid
comprises only said first microphone and said second microphones,
and wherein the step of identifying said less sensitive microphone
comprises identifying an operational sign of said deviation of said
average values from each other.
14. A method as claimed in claim 9 comprising the additional steps
of monitoring a level of said output signals of said microphones
and conducting the step of identifying any deviation of said
average values from each other only when said level of said output
signals exceeds a predetermined level.
15. A method as claimed in claim 14 comprising the additional step
of, when said level of said output signals is below said
predetermined level, identifying and storing a plurality of optimum
amplification values for said output signals of said first and
second microphones and wherein the step of amplifying at least one
of said output signals of said first and second microphones
comprises using one of said stored optimum values.
16. A method as claimed in claim 9 wherein said output signals of
said first and second microphones exhibit a frequency which varies
within a frequency range, and wherein the step of identifying any
deviations of said average values from each other comprises
identifying any deviations of said average values from each other
in an adjustable frequency range within said frequency range of
said output signals of said first and second microphones.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a hearing aid of the type
having two microphones with automatic balancing of the output
signals of the respective microphones, as well as to a method for
operating such a hearing aid.
2. Description of the Prior Art
Hearing aids are known wherein a subtraction of the signals of two
omni-directional microphones ensues for producing a directional
microphone characteristic. The desired directional microphone
characteristic of the hearing aid arises due to the phase
difference which occurs as a result of the different transit times
of the microphone signals.
In order to achieve a directional microphone characteristic, the
two microphones of the hearing aid must exhibit identical frequency
responses and sensitivities. It is therefore necessary to employ
microphone pairs and microphone groups that are specifically
selected and adapted to one another. Nevertheless, an undesired
shift of the directional microphone characteristic due to different
post-assembly modification of the characteristics of the individual
microphones, for example due to aging, temperature or radiation
influences, cannot be avoided.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hearing aid as
well as a method for the operation of a hearing aid wherein an
undesired change of the directional microphone characteristic of
the hearing aid is avoided.
In the inventive hearing aid and method, a first difference element
is used to subtract the respective signals from two microphones,
with the output of this first difference element being supplied to
the earphone of the hearing aid, and a subtraction of average
values of the output signals of the microphones ensues with a
second difference element. Proceeding from the identified deviation
of the average values of the output signals of the microphones, the
amplification of the output signal of at least one of the
microphones is regulated by an analysis/control unit following the
second difference element until no deviation of the average values
of the output signals of the microphones subtracted from one
another can be found following the second difference element.
This makes it possible to combine more economical microphones that
are not precisely adapted to one another into microphone pairs or
microphone groups in a hearing aid, and to recognize and eliminate
the differences of the characteristics of the microphones, for
example in the frequency response or in the sensitivity, that exist
from the very start or occur during the useful life.
The manufacturing costs are lowered by expanding the combination
possibilities of different microphones. Further, modifications in
the characteristics occurring during the useful life of the
microphones can be recognized and corrected, so that a uniformly
high microphone quality and accurate directional microphone
characteristic is achieved over the entire service life of the
hearing aid.
In one embodiment, an adjustable amplifier element for controlling
the amplification of the corresponding output signal is allocated
to at least one of the microphones.
Average values of the output signals of the microphones are
subtracted from one another in the second difference element of the
inventive hearing aid. The output signals of the microphones are
preferably rectified before being supplied as input signals to the
second difference element.
In another embodiment, the analysis/control unit is an I-regulator,
so that a constant repetitive error is not obtained in the control
event. For further stabilization of the control event, the
analysis/control unit can be a PI regulator.
The level of the output signals of the microphones and/or of the
output signal of the second difference element can be acquired via
a level acquisition element such as a threshold element, in order,
for example, to cut-in the automatic microphone balancing only
after upward transgression of a minimum level.
In another embodiment, the output signals of the microphones pass
through a filter element (for example, a low-pass filter or a
bandpass filter) with which the control event of the inventive
hearing aid is activated in an identified frequency range.
In the inventive method, average values are initially formed
proceeding from the output signals of the microphones.
Subsequently, the deviation of the average values from one another
is identified and the amplification of at least one of the output
signals of a microphone is potentially controlled as needed in
order to reduce the deviation of the average values and,
ultimately, to eliminate it.
For example, the RMS values (root mean square) or peak values can
be employed as average values of the output signals. A balancing of
the RMS values is more complicated but is also more precise,
whereas a balancing of the peak values can ensue within a shorter
time.
In an embodiment of the method, the amplification, in particular,
of the less sensitive microphone is boosted when a deviation of the
average values from one another is found. The less sensitive
microphone given a hearing aid with two microphones can be
identified on the basis of the operational sign of the deviation of
the average values.
The signal amplification of a number of microphones can be adjusted
in the same or opposite directions for automatic microphone
balancing.
In order to avoid the intrinsic low level noise of the microphones
from being amplified, the inventive method for the automatic
microphone balancing can be activated only when an adjustable
minimum level is upwardly transgressed.
When this level is downwardly transgressed, an optimum
amplification (gain value) for the output signals of the individual
microphones that has already been identified or stored can be set.
The optimum individual amplification of the output signals of the
microphones is again individually identified only when the limit
level value is exceeded.
In order to avoid distortions, it can also be advantageous not to
implement any automatic microphone balancing outside of an
identifiable frequency range. Thus, for example, the inventive
method can be implemented only in a specific frequency range on the
basis of a bandpass filter.
DESCRIPTION OF THE DRAWINGS
The single FIGURE is a block circuit diagram of a hearing aid with
automatic balancing of the output signals of the microphones,
constructed and operating in accordance with the principles of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The drawing shows a schematic circuit diagram for a hearing aid
having two microphones 1a and 1b whose output signals are supplied
to a first difference element 3 via adjustable amplifier stages 2a
and 2b. The output signal of the first difference element 3 has a
directional characteristic and is further-processed in a signal
processing unit 4 in order to be supplied to an earphone 5.
Inventively, the output signals of the two amplifier stages 2a and
2b are also supplied to a second difference element 9 via two
rectifier stages that are respectively composed of balancing
elements 6a, 6b, absolute value-forming units 7a, 7b and filters
8a, 8b. Following the two rectifier stages, which can also be
fashioned with digital components, the output signals are
subtracted from one another in the second difference element 9 in
order to identify any deviation therebetween. Different average
values of the output signals (for example, RMS values or peak
values) can be generated via further signal processing elements
preceding the second difference element 9.
The output signal of the second difference element is supplied to
analysis/control units 10 and 11 in order, via a corresponding
control of one or both amplifier stages 2a and 2b, to reduce the
deviation of the average values found subsequently in a second
subtraction in the second difference element 9, and ultimately to
eliminate any deviation. A further signal analysis of the output
signal of the second difference element 9, for example with
reference to further parameters, can also ensue in the
analysis/control units 10 and 11 in order, for example, to select a
suitable type of regulator (for example I-regulator).
The analysis/control units 10 and 11 also can be connected to the
signal processing unit 4 with signal lines (not shown) in order to
achieve an optimization of the overall signal processing in the
hearing aid via a data exchange.
Via a filter element (not shown), an adjustable frequency range of
the output signals of the amplifier stages 2a and 2b is supplied to
the second difference element 9, so that, for example, especially
high or especially low frequencies can be blanked out. An undesired
distortion that can occur given automatic microphone balancing in
these limit frequency ranges is thus avoided.
Via a threshold element, a determination can be made in the level
acquisition element 12 to activate the automatic microphone
balancing by the control in the analysis/control units 10 and 11
only beginning at a specific minimum level, in order to avoid
amplification of the intrinsic noise of the microphones 1a and 1b
at low levels.
Alternatively, only a single analysis/control 10 can also be
provided, this being connected (not shown) to both amplifier stages
2a and 2b.
A filter element (not shown) and the level acquisition element 12
can be connected in common with the second difference element 9 and
the analysis/control units 10 and/or 11 in order to achieve a
corresponding overall balancing (not shown) of the automatic
microphone balancing.
Although modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of his contribution
to the art.
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